1. Field of the Invention
The present invention concerns a reversible preloading device for bearings for mounting blades on a propeller hub.
2. Description of Related Art
Propellers for turbo-prop airplanes require a maximum degree of operation. For this, there are systems for holding the blades on the hub whose principle permits rapid disconnection from and reconnection to the plane without having to remove the propeller.
Two types of solutions exits.
The first, used on propellers of type 24F, 568F and NP2000, consists of having one or more rows of ball bearings, which are preloaded automatically by centrifugal force when the propeller is placed in rotation.
When the power of the propeller increases and when the forces on the blade became great, a second type of solution is used that consists of preloading the bearings of the blade base, as shown, for example, in document U.S. Pat. No. 4,850,801. However, in these solutions, there is a risk of great variation of the preloading and it may even be lost due to the rigidity of the system and thermal variations; on the other hand, all the parts coming in contact are subjected to vibration, with risks of contact wear (“fretting” in English). Document U.S. Pat. No. 5,118,256 discloses an improvement using an elastomer block for preloading to partially eliminate these problems, but the system has a limited service life, inducing high maintenance costs. Moreover, these solutions have another major defect, i.e., the necessity of having complex disconnection tools.
In order to alleviate this defect, document U.S. Pat. No. 6,213,719 proposes having recourse in an entirely different system of blade mounting, i.e. mounting by pins.